Stabilizing composition for a metal deposition process

ABSTRACT

A method for depositing a metal on a surface is disclosed. The method comprises treating the surface with a sensitizing solution comprising at least a reducible salt of a non-noble metal and a radiation-sensitive reducing agent for the salt to form a sensitized surface. The sensitized surface is exposed to a source of light radiation to reduce the metal salt to a reduced metal salt species. Either or both of the preceding sensitizing or radiation exposing steps is restricted to a selected pattern on the surface to form a catalytic real image capable of directly catalyzing the deposition of a metal thereon from an electroless metal deposition solution. The catalytic real image is treated with a stabilizer comprising (a) a reducing agent for the non-noble metal ions of said reducible salt, (b) a complexing agent and (c) an accelerator to at least stabilize the catalytic real image.

This is a division, of application Ser. No. 848,001 filed Nov. 3, 1977,now U.S. Pat. No. 4,133,908, issued Jan. 9, 1979.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a stabilizing composition for use in a methodof depositing a metal on a surface and more particularly, to astabilizing composition for use in a method of selectively depositing anelectroless metal deposit on a surface.

2. Discussion of the Prior Art

Heretofore, it has been known to employ a number of pretreatment ofsensitization baths in effecting the electroless deposition of metals onvarious surfaces. Typically, such prior art sensitization baths usedcommercially have been expensive because they depend upon a noble metal,e.g., Pd, Pt, Ag, Au, etc., as the sensitizing component. However,recently methods have been reported in which electroless metal depositscan be applied to a broad variety of insulating substrates without theneed to use expensive noble metals but on the contrary, employ reduciblesalt compositions of non-noble metals. U.S. Pat. Nos. 3,772,056;3,772,078; 3,907,621; 3,925,578; and 3,930,963 disclose such methods. Aproblem with the methods disclosed in these patents and not recognizedor addressed thereby or therein is that of moisture or humidity whichaffects a catalytic real image formed by the methods and the resultantelectroless metal deposit.

The above-described problem has been recognized and obviated by aprocess revealed in U.S. patent application Ser. No. 714,455, now U.S.Pat. No. 4,084,023, filed by R. V. Dafter, Jr. on Aug. 16, 1976, andentitled "A Method of Depositing a Metal on a Surface," and assigned tothe assignee hereof. In this method the real image is treated with afixing solution comprising an autocatalytic reducing agent, e.g.formaldehyde where the real image comprises a copper species. Althoughthe real image after treatment with such a fixing solution issuccessfully stabilized with respect to ageing and/or high humidityconditions, it has been found that upon subsequent treatment with anelectroless plating solution the resultant electroless deposit upon thereal image becomes smeared and tends to spread or in general to degrade.This condition occurs with real images which have been stabilized withthe fixing solution of the aforementioned Dafter application as well aswith those real images which have not been treated or stabilized withthe fixing solution, such as the real images obtained with theabove-identified U.S. patents.

Accordingly, a method of preventing the smearing or spreading of anelectroless metal deposit on the real image is needed and is an objectof this invention.

SUMMARY OF THE INVENTION

This invention relates to a method of depositing a metal on a surfaceand more particularly, to a method of selectively depositing anelectroless metal deposit on a surface.

The method of depositing a metal on a surface includes coating thesurface with a sensitizing solution comprising at least a reducible saltof a non-noble metal and a radiation sensitive reducing agent for thesalt to form a sensitized surface. The sensitized surface is exposed toa source of light radiant energy to reduce the metal salt to a reducedmetal salt species, wherein the sensitizing and/or exposing steps arerestricted to a selected pattern on the surface to form a catalytic realimage capable of directly catalyzing the deposition of a metal thereonfrom an electroless metal deposition solution. The catalytic real imageis treated with a stabilizer comprising a reducing agent for thenon-noble metal ions of the reducible salt, a complexing agent and anaccelerator to at least stabilize the catalytic layer.

DETAILED DESCRIPTION

The present invention will be discussed primarily in terms ofselectively depositing copper on a surface of a substrate. It will bereadily appreciated that the inventive concept is equally applicable todepositing other suitable metals which are catalytically reduced fromtheir respective ions by the catalytic surface areas produced by thesubject invention. It will also be appreciated that the selectivedeposition is not limited to any one particular type of surface but isapplicable to metallizing any surface whether used as a printed circuitboard or not.

The present invention relates to imposing by radiant energy sensitive,non-conductive areas on the surfaces of a substrate which catalyze thedeposition of strongly adherent and continuous deposits of electrolessmetal. U.S. Pat. Nos. 3,772,056; 3,772,078; 3,907,621; 3,925,578; and3,930,963, all of which are incorporated hereinto by reference, disclosea method of selectively metallizing a surface by coating with acomposition comprising at least a reducible salt of a non-noble metalselected from copper, nickel, cobalt or iron, and a radiation-sensitivereducing agent for the salt. The coated composition is then converted,by reduction of the salt by exposure to a source of radiant energy, tocomprise electrically non-conductive reduced metal species nuclei,believed to be metal nuclei, capable of catalyzing the depositionthereon of a metal from an electroless metal deposition solution.However, it has been found that the method (exposure to radiant energy)disclosed in the above-identified patents, incorporated by referencehereinto, does not successfully work in that when the radiation-exposedsurface is subsequently metallized by exposure to an electroless metaldeposition solution, the resultant electroless metal deposit is smearedor runs or bleeds from the boundaries of the real image. It ishypothesized that this smearing or bleeding is due to the leaching outof the real image of unreacted portions of the radiation-sensitivereducing agent or reacted (oxidized) species of the radiation-sensitivereducing agent. It is of course to be understood that the above is ahypothesis only and the subject invention is not to be restricted in anymanner thereby. Of course, the subject invention obviates the bleedingproblem regardless of what causes it.

A suitable substrate is first selected. Typical suitable substratesinclude bodies comprising inorganic and organic substances, such asglass, ceramics, porcelain, resins, paper, cloth and the like. Forprinted circuits, among the materials which may be used as the bases,may be mentioned dielectric coated metal or unclad insulatingthermosetting resins, thermoplastic resins and mixtures of theforegoing, including fiber, e.g., fiberglass, impregnated embodiments ofthe foregoing.

Porous materials, comprising paper, wood, fiberglass, cloth and fibers,such as natural and synthetic fibers, e.g., cotton fibers, polyesterfibers, and the like, as well as such materials themselves, may also bemetallized in accordance with the teachings herein. The invention isapplicable to the metallization of resin-impregnated fibrous structuresand varnish-coated, resin-impregnated fiber structures of the typedescribed.

Since radiant energy, such as ultraviolet radiation, is to be employed,suitable substrates include those which are opaque to the transmissionof radiant energy. This prevents "printing through" and also facilitatessimultaneous or sequential formation of images and circuits on bothmajor surfaces of the board. The substrate surfaces can be renderedopaque to light energy mechanically, i.e., by frosting with sandblastingand the like, or chemically by etching with appropriate reagents, suchas chromic acid for resins and hydrogen fluoride for glass, alkali forporcelain, and the like. Frosted surfaces will scatter rather thanabsorb incident energy. On the other hand, energy absorbing substancescan be dispersed in the substrate or adsorbed on the surface thereof torender the substrate opaque. By way of illustration, pigments, such ascarbon black and titanium dioxide, are useful to prevent penetration bylight in the visible wavelengths; bismuth, tin, lead and thoriumcompounds, as well as organic iodine compounds are useful as X-rayradiation and electron barriers. Lead compounds are useful neutronshields. The substrate can be rendered opaque to light energy,particularly at visible or ultraviolet wavelengths with a conventionalcompound, such as hydroxy benzophenone, a hydroxy benzotriazole or asubstituted acrylate, and the like.

A surface of the substrate is selectively deposited with an electricallynon-conductive layer or real image comprising nuclei of a metal species,typically the metal, which is capable of catalyzing the deposition ofelectroless metal from an electroless metal deposition solution withwhich it is destined to be exposed or treated.

The real image typically comprises metal species nuclei, e.g., metalnuclei, in which the metals are selected from Groups VIII and IB of thePeriodic Table of Elements. Preferred metals are selected from Period 4of Groups VIII and IB; iron, cobalt, nickel and copper. Especiallypreferred for the production of the real image is copper.

If desired the surface can be coated with an adhesive before beingcoated with the compositions of this invention.

In producing the real image, the metal species nuclei are reduced fromtheir salt or a composition of the salt in situ in selected areas on thesurface of the substrate by application of light radiant energy, such asultraviolet light and visible light, X-rays, electron beams, and thelike.

The reducible metal salt can comprise, in general, a cation selectedfrom the metals of Group VIII and IB of the Periodic Table of theElements. The anion associated in such metal salts can vary widely andcan comprise organic and inorganic anions such as halides, sulfates,nitrates, formates, gluconates, acetates and the like. The cations insuch salts will include copper, nickel, cobalt and iron, in any of theusual degrees of oxidation, e.g., both cuprous and cupric, ferrous andferric, etc., will serve. Some typical salts include cupric formate,cupric gluconate, cupric acetate, cupric chloride, cupric nitrate,nickel chloride, cobalt chloride, ferrous sulfate and cobalt chloride.

The surface of the substrate, if necessary, is cleaned as described inthe patents incorporated hereinto by reference. A sensitizing solutionof a reducible metal salt composition, e.g., cupric formate, and a lightradiant energy-sensitive reducing agent contained in a suitable solvent,e.g., water, an alcohol, mixtures of water and an alcohol (ethanol,butanol, etc.), dimethylformamide, dimethyl sulfoxide, is applied to thesurface to form a sensitizing solution layer. The coated surface istypically dried and then exposed through a positive or negative of anoriginal pattern or photograph, to form the real image on selectedportions of the surface. The real image comprises reduced metal saltspecies nuclei, e.g., copper metal nuclei.

The radiant energy sensitive compound used in association with thereducible metal has the property of decomposing to a compound which willexercise a reducing action on the exposed metal salt. Preferredradiation sensitive compounds are anthraquinone and derivatives thereof,such as 9,10-anthraquinone, β-chloroanthraquinone,β-phenylanthraquinone, 1,2-benzanthraquinone, anthraquinone-2-sulfonicacid, anthraquinone-2,6 (or 2,7-)-disulfonic acid and salts thereof, andanthraquinone 2,6-disodium sulfonate, anthraquinone-2,7-disodiumsulfonate, anthraquinone-2,7-dipotassium sulfonate, and the like.Particularly preferred are the anthraquinone disulfonic acids and thesalts thereof.

A preferred additional ingredient in the treating composition is asecondary reducer, such as an organic, oxygen- or nitrogen-containingcompound. Such an ingredient serves to facilitate interaction of radiantenergy and the radiant energy-sensitive compound to provide a reductionof the metal salt to the free metal nuclei. Although the secondaryreducer compound may be any oxidizable organic compound which is solublein the solution, does not attack the base material, and is inert to theother ingredients, it is preferred that it comprise a hydroxy compoundsuch as an alcohol or a polyol. Especially preferred as secondaryreducing compounds are alcohols or polyols. Among the organic oxygenatedcompounds can be mentioned glycerol, ethylene glycol, pentaerythritol,mesoerythritol, 1,3-propanediol, mannitol, 1,2-butanediol, pinacol,sucrose, dextrin, polyethylene glycols, lactose, starch, gelatin, andthe like. Also included are compounds such as triethanolamine andpropylene oxide. Compounds which are also useful as secondary reducersare amino compounds, polyethers, certain dyestuffs and pigments. Amongthese may be mentioned aldehydes, such as formaldehyde, benzalhyde;acetaldehyde; N-butyraldehyde, polyamides, such as nylon, albumin andgelatin; leuco bases of triphenylmethane dyes, such as4-dimethylaminotriphenylmethane; leuco bases of xanthene dyes, such as3,6 -bisdimethylaminoxanthane and3,6-bisdimethylamino-9-(2-carboxyethyl)xanthene; polyethers, such asethylene glycol diethyl ether, tetraethylene glycol dimethylether,alizarin, erythiocin, phthalocyanine blue, zirconium silicate and thelike. A preferred secondary reducer is sorbitol.

Additionally, other ingredients known as metal reductionintensifiers/accelerators/stabilizers, described in the patentsincorporated hereinto by reference, may be added to the treatingsensitizing solution to provide desired effects, such as to speed-up theexposure time, help bring out the real image and provide bettercontrast, provide anti-fogging, etc. For example, image formation can beaccelerated; contrast can be improved, and the stability of the imageenhanced if to the solution comprising the metal salt and radiantenergy-sensitive compound are added halogens, e.g., bromides andchlorides, alone or in combination with metals such as tin, alkalimetals, mercury, germanium, titanium, molybdenum, rare earths, amines,ammonia and the like. Illustrative of such compounds are: hydrogenhalides and alkali metal or alkaline earth metal halides, ammonia oramine halides and the like. In some embodiments the recited compoundsmay be used with organic acids such as mono-, di-, tri-carboxylic acidsor salts thereof and the like, for example, with acetic acid, citricacid, oxalic acid and the like.

A particularly effective additive has been found to be ferrithiocyanidecompounds, e.g., potassium ferrithiocyanide.

In addition to the metal reduction imageintensifiers/accelerators/stabilizers, the composition comprising themetal salt and the radiant energy-sensitive compound can include also asurfactant, for those surfaces which are hard to wet with the particularsensitizing solution employed. The choice of the surfactant is notparticularly critical, but usually it is preferred to use a non-ionicsurfactant, because this permits a broader range in formulation. Amongthe suitable surfactants are polyethyleneoxy non-ionic ethers such asTriton-X 100, manufactured by Rohm & Haas Company, and non-ionicsurfactants based on the reaction between nonylphenol and glycidol suchas surfactants 6G and 10G manufactured by the Olin Company. Alsosuitable are fluorocarbon surfactants such as perfluorodecanoic acid andthe series of related compounds manufactured by the 3M Company under theproduct designation FC-170 and the like.

The treating sensitizing solution may be formulated within broadconcentration ranges, depending primarily on the relative amount ofmetal salt composition desired to be placed on the surface, which inturn will depend on the mode of application, e.g., immersion, dipcoating, roller coating, curtain coating, spraying and the like. Inaddition, the concentration of the ingredients in solution will belimited by solubility in the solvent. In general, the metal saltconcentration will be predetermined and the amounts of radiantenergy-sensitive compound and other ingredients, if present, will beadjusted to provide a ratio which will insure the desired result. Thisis well within the skill of those familiar with the art of formulatingradiant energy-sensitive systems. For example, at least enough radiantenergy-sensitive compound will be present to facilitate substantiallycomplete reduction by exposure to radiant energy of the metal salt tothe free metal nuclei. Usually to insure complete reduction, asubstantial excess of the radiant energy-sensitive compound (based onthe reducible metal ions) will be present. The metal salt concentrationin solution can vary over wide limits, e.g., from 0.5 to 100 grams ormore per liter can be used but it is most convenient and economical notto use more than about 25 grams per liter and preferably less than about15 grams per liter. The radiant energy-sensitive compound can comprisefrom about 1 to 10 or more equivalents, based on the metal salt. Theamount of the secondary reducer, e.g., glycerol, sorbitol,pentaerythritol, dyestuff or the like, can likewise vary over a widerange, e.g., from 0.5 to 500 grams per liter, but in the case ofdifficult to volatilize liquid compounds, it is preferred not to includeso much of such compounds that the treated surface is wet or sticky tothe touch after drying. The ingredients, such as halide ions, stannoushalides and carboxylic acids added to the compositions as for exampleimage intensifiers, will generally be used in relatively lowconcentrations, e.g., from trace amounts, e.g., from about 1 mg. perliter up to about 2 grams per liter. The amount of ferrithiocyanidecompounds ranges from 50 to 150 parts per million. Surfactants will beused in small, but conventional quantities, if present. The non-ionicswill be used at levels from about 0.1 to 2 grams per liter and anionicsfrom about 0.1 to 1.0 gram per liter.

The resultant real image is catalytic to electroless metal depositionand can be processed in known ways for the subsequent build-up ofelectroless metal plating and, optionally, a top layer ofelectroplating. Heretofore, the surface having the real image thereonwas rinsed in running water to remove the light radiation energyunexposed portions of the non-noble metal ions and then immersed in asuitable electroless metal deposition solution to deposit an electrolessmetal thereon. However, it has been found that the electroless metaldeposit deposited on the real image is smeared or has bled beyond theboundaries of the real image. It has surprisingly been found that such aproblem can be eliminated by treating the real image with a stabilizerwhich stabilizes the real image and prevents the smearing or bleeding ofan electroless metal deposit from occurring thereon. The real imagecontaining surface is treated with the stabilizer prior to removing theradiation unexposed or unreduced portions of the sensitizer layer or theradiation unexposed or unreduced portions of the non-noble metal ionsfrom the background of the surface, such as by water rinsing, and priorto exposing the real image to an electroless metal deposition solution.

After exposure to the light radiant energy source, the real image istreated with a suitable stabilizer. A suitable stabilizer typicallycomprises a solution comprising (a) a reducing agent for the non-noblemetal ions of the metal salt contained on the surface, (b) a complexingor chelating agent, (c) an electroless metal accelerator and (d) a basiccompound, where the real image comprises a copper species. The solventemployed in the stabilizer solution is a chemically inert solvent whichmay be either aqueous or non-aqueous. Preferably, the solvent compriseswater. It is to be stressed hereat that surprisingly and unexpectedly,the stabilizing effect which prevents electroless metal depositionbleeding is not attained unless the stabilizer comprises the combinationof the reducing agent, the chelating agent and the accelerator and inthe case where a copper species containing real image is formed, thecombination must additionally contain a basic compound, e.g., NaOH, KOH.

The reducing agent includes a selective reducing agent which reduces ametal ion, e.g., Cu⁺², to its corresponding metal, e.g., Cu°, by thepresence of the corresponding metal (catalyst), e.g., Cu°. Suchselective reducing agents are well known in the art of electroless metaldeposition. Where copper salts are used in the sensitizing solution ofthe subject invention, typical selective reducing agents include, underalkaline aqueous conditions (pH>7), formaldehyde and paraformaldehyde.Where nickel and cobalt salts are used in the sensitizing solution ofthe subject invention, typical reducing agents include, under alkalineaqueous conditions (pH>7), formaldehyde and paraformaldehyde, and underacidic aqueous conditions (pH<7) hypophosphite species, e.g., sodiumhypophosphite, potassium hypophosphite, etc.

What reducing agents are suitable with respect to a particular metal ionand the conditions for such a reduction are easily ascertainable bythose skilled in the art, without an undue amount of experimentation, inthe light of the disclosure contained herein.

The reducing agent is present in an amount sufficient to reduce thenon-noble metal ions contained in the real image which were not reducedby the radiant exposure. Typically, the reducing agent is present in anamount ranging from 0.7 to 1.4 weight percent of the resultantstabilizer solution.

The reducing agent selectively reduces those non-noble metal ionscontained in the real image which were not reduced by the radiant energyexposure thereby reinforcing the real image. It appears that only thoseions contained within the real image are so reduced since only thereduced non-noble metal salt species, e.g., copper metal, containedwithin the real image catalyzes the reduction. Areas other than theradiant energy exposed areas or the real image areas contain non-noblemetal ions but do not contain the reduced non-noble metal, e.g., coppermetal, and therefore are not so reduced by the reducing agent.

Suitable complexing or chelating agents include any conventionalcomplexing agent employed in an electroless metal deposition solution.Some suitable complexing agents include ethylenediaminetetraacetic acidand the sodium mono-, di-, tri-, and tetrasodium salts thereof,N-hydroxyethylenediamine triacetate, triethanolamine and N, N, N', N'tetrakis-(2-hydroxypropyl) -ethylenediamine. Other conventionalcomplexing agents may readily be found by those skilled in the art byreference to standard works, such as, for example, W. Goldie, MetallicCoating of Plastics, Electrochemical Publications, Limited, Middlesex,England, 1968. The concentration of the complexing or chelating agent isnot critical. The complexing agent should be present in an amountsufficient to complex any free metal, e.g., copper, contained on thesurface containing the real image. Typically, the complexing agent ispresent in an amount ranging from 2.8 to 4.7 weight percent of theresultant stabilizer solution.

Suitable accelerators are water-soluble complex cyano-metallo compoundsin which the cyanide radical (CN⁻) is complexed with certain metals ofGroup 8 of the Periodic Table of Elements as set forth in the MendelyeevPeriodic Table appearing on page B2 in the 45th edition of the Handbookof Chemistry and Physics published by the Chemical Rubber Company,including mixtures of such compounds. These accelerators are describedin U.S. Pat. No. 3,485,643, incorporated hereinto by reference. Typicalof such compounds are those in which the cyanide radical (CN⁻) iscomplexed with iron, iridium and rhenium, including mixtures of suchcompounds.

Preferred for use are the water-soluble complex cyano-iron compounds,i.e., hexacyanoferrate (II) and hexacyanoferrate (III) compounds, aswell as mixtures of such compounds. Typical of such compounds are theferricyanides and ferrocyanides of the metals of Groups 1a (alkalimetal) and 2a (alkaline earth metal) of the Periodic Table of Elements,referred to above, and ammonium. Preferred for use are the sodium,potassium and ammonium ferricyanides and ferrocyanides. It will beappreciated that in alkaline solutions the ferricyanides will be reducedto ferrocyanides, so that in such solutions the ferrocyanides willfunction as the accelerator, even though the accelerator is added as aferricyanide. The accelerators are present in an amount sufficient toimpart with the other components the bleed stabilization required.Typically the accelerator is present in amount ranging from 0.19 to 0.75weight percent of the resultant stabilizer solution.

Where a reducible copper salt is employed to obtain the real image, thestabilizer must contain in combination with the reducing agent, thecomplexing agent and the accelerator a basic compound. Any basiccompound which is chemically compatible with the other components of thestabilizer can be employed. Typically, alki metal compounds, e.g., NaOH,Na₂ CO₃, KOH, ammonium hydroxide and amines are employed. The amount ofbasic compound employed is not critical and typically is present in anamount ranging from 0.9 to 1.2 weight percent of the resultantstabilizer solution. However, in the case of a real image containing acopper species, the pH of the resultant stabilizer solution should beabove 7 and preferably 12.5 to about 12.8 whereby optimum bleedstabilization is obtained.

It is again to be pointed out and stressed that using a solution whichdoes not contain the combined components of (a) the reducing agent, (b)the complexing agent, (c) the accelerator and optionally (d) the basiccompound (in the case of a real image containing a copper species), willnot lead to a bleed stabilization.

It is also to be pointed out and stressed hereat that the stabilizingsolution is not an electroless metal deposition solution. Thestabilizing solution does not contain additional non-noble metal ions,e.g., Cu⁺², Ni⁺², etc., along with the reducing agent, the complexer,the accelerator and optionally the basic compound. The only non-noblemetal ions which are present and which are reduced are those alreadycontained on the surface of the substrate and in particular those ionscomprising and contained within the boundaries of the real image.

The surface containing the real image is treated, e.g., by immersion,with the stabilizer for a period of time, e.g., typically 4 minutes andat a temperature, e.g., typically 38° C., to bleed stabilize the realimage.

The stabilizer solution serves another purpose besides bleed stabilizingthe real image, it serves to wash out or remove the unexposed (as wellas unstabilized) portions of the sensitizing layer. Thestabilizer-treated real image surface can be directly immersed ortreated with an electroless metal deposition solution without additionalrinsing steps. However, preferably, the bleed stabilized surface iswater rinsed or rinsed with any other inert rinsing agent, e.g.,typically for 0.5 minute at 25° C. and then treated with an acidstripping solution such as described in copending U.S. patentapplication, Ser. No. 831,824, filed on Sept. 9, 1977, assigned to theassignee hereof. Such an acid solution comprises an organic acidselected from (a) an acid having the structural formula ##STR1## where Ris the hydrogen atom, H, or an alkyl radical having 1 to 5 carbon atoms,e.g., formic acid, acetic acid; (b) citric acid and (c) a mixture of (a)and (b). The surface is typically treated with the acid solution for aperiod of time ranging from 10 seconds to 3 minutes at 25° C. wherebyessentially all of the remaining unexposed portions of the sensitizinglayer (if any) are removed thereby. The use of the stripping solutionaids in preventing physical removal or smearing as through physicalhandling of the real image during electroless metallization thereof. Thebleed stabilized image containing surface (which may or may not be waterrinsed and acid treated) is then immersed in a suitable electrolessmetal deposition solution to deposit an electroless metal deposit on thefixed image.

Suitable electroless metal deposition solutions are well known in theart and will not be elaborated herein. Reference in this regard is madeto the patents incorporated hereinto by reference, which disclose somesuitable electroless metal deposition solutions.

The electroless metal deposit may be built up to a desired thickness byprolonged exposure to the electroless metal deposition solution or,alternatively, may be further built up by being electroplated in astandard electroplating bath. Again, the various typical electroplatingsolutions, plating conditions and procedures are well known in the artand will not be elaborated herein. Again, reference in this regard ismade to U.S. Pat. Nos. 3,772,056; 3,772,078; 3,907,621; 3,925,578; and3,930,963, incorporated hereinto by reference.

In an alternate embodiment, the surface of the substrate is imprinted orselectively stamped with the sensitizing solution. The surface is thenexposed to the source of radiant energy to form the real image. The realimage is then bleed stabilized on the surface with the stabilizersolution. The bleed stabilized, imaged surface may then be water andacid rinsed and is then immersed or treated with the electroless metaldeposition solution.

It is of course to be understood that the substrate may be blanketmetallized, the substrate being dip coated with the sensitizing solutioncomprising at least the reducible metal salt and the light-sensitivereducing agent for the salt. The coated substrate is then exposed to aradiant energy, e.g., ultraviolet radiation, source to form a catalyticsurface. The catalytic surface is treated by immersion in a bathcomprising the stabilizer solution and then electrolessly metaldeposited. If it is desired to pattern the metal deposit, conventionalsubtractive techniques can be employed, such as conventional masking andetching techniques.

EXAMPLE I

For comparison purposes, a substrate comprising a steel core with afully cured diglycidyl ether of bisphenol A coating thereon wasselected. The substrate comprised about 200 through holes having adiameter of about 0.050 inch. The substrate was immersed in a solventbath comprising a mixture of 90 volume percent methyl ethyl ketone and10 volume percent methanol for ten minutes at 25° C. The substrate waswater rinsed for one minute at 25° C. and then etched in an aqueoussolution comprising 300 grams CrO₃ and 250 grams H₂ SO₄ in 1000 ml. ofwater, maintained at 25° C. for ten minutes. The etched substrate wasthen water rinsed at 25° C. for ten minutes.

A sensitizing solution was prepared by dissolving 10 grams of cupricacetate, 4 grams of 2,6-anthraquinone disulfonic acid disodium salt, and50 grams of sorbitol in a solvent comprising 950 ml. of H₂ O. The etchedsubstrate was immersed in the sensitizing solution for one minute at 25°C., removed therefrom and dried at 50° C. for two to four minutes. Asurface of the dried substrate was selectively exposed to ahigh-pressure mercury discharge lamp (30 watts/cm² surface at 3660A.)for 90 seconds to form a real image. The imaged surface was then waterrinsed at 25° C. for 0.5 minute. The surface was then immersed in aconventional electroless metal deposition solution comprising cupricsulfate, formaldehyde, sodium cyanide, alkali andethylenediaminetetraacetic acid for 15 minutes at 35° C. A smeared, 50μinch thick electroless copper pattern which extended in part beyond theboundaries of the real image, that is a deposit which bled or ran fromthe real image, was obtained.

EXAMPLE II

For comparison purposes, the procedure of Example I was repeated exceptthat after the real image was formed, the imaged surface was firsttreated by immersion for 5 minutes at 25° C. in an aqueous strippingsolution comprising 5 weight percent acetic acid of the resultantsolution. The stripping solution treated surface was then water rinsedat 25° C. for 0.5 minute. Upon treatment with the electroless metaldeposition solution, a smeared electroless copper deposit as in ExampleI, was obtained.

EXAMPLE III

For comparison purposes, the procedure of Example I was repeated exceptthat after the real image was formed, the imaged surface was immersed inan aqueous solution comprising (1) 200 ml. of a 40 weight percentaqueous solution of ehtylenediaminetetraacetic acid, (2) 80 ml. of a 37weight percent aqueous solution of formaldehyde, (3) 64 ml. of a 10Naqueous NaOH solution and (4) 1636 ml. of water. The surface wasimmersed in the solution at 38° C. for 4 minutes whereafter it was waterrinsed at 25° C. for 0.5 minute, and then treated with the electrolessmetal deposition solution. A smeared, 50 micro-inch thick electrolesscopper patern, similar to that obtained in Example I, was obtained after15 minutes of immersion in the electroless copper solution.

EXAMPLE IV

The procedure of Example III was repeated except that the aqueoussolution comprised (in addition to the formaldehyde, theethylenediaminetetraacetic acid and the NaOH), 20 ml. of a 20 weightpercent aqueous solution of K₄ Fe(CN)₆. The real imaged surface wasimmersed in the resultant stabilizing solution at 38° C. for 4 minutes,water rinsed at 25° C. for 0.5 minute and then treated with theelectroless metal deposition solution. A 50 micro-inch thick electrolesscopper pattern, deposited on the real image was obtained after 15minutes of immersion in the electroless copper solution at 35° C. Thecopper pattern did not exhibit any smearing, running or bleeding outsidethe original boundaries of the real image as evidenced by examinationwith a microscope at a 30 fold magnification.

EXAMPLE V

The procedure of Example IV was repeated except that after the realimaged surface was treated with the stabilizing solution and waterrinsed, it was then immersed in an aqueous stripping solution comprising5 weight percent acetic acid for 5 minutes at 25° C. The surface wasthen water rinsed at 25° C. for 0.5 minute and immersed in theelectroless copper deposition solution. A 50 micro-inch thickelectroless copper pattern which did not spread from the boundaries ofthe real image was obtained, as in Example IV.

EXAMPLE VI

A. The procedure of Example IV was repeated except that the real imagedsurface was immersed in the stabilizing solution for 4 days. The realimage did not degrade or fade. Thus the stabilizing solution acts as aninventorying expedient whereby the real image is protected from fadingor degradation.

B. For comparison purposes the procedure of Example VI-A was repeatedexcept that the real image surface was not immersed in the stabilizingsolution, but in water. After one minute the real image began to fadeand disappear.

It is to be understood that the above-described embodiments are simplyillustrative of the principles of the invention. Various othermodifications and changes may be made by those skilled in the art whichwill embody the principles of the invention and fall within the spiritand scope thereof.

What is claimed is:
 1. A stabilizing composition for a real imagecomprising a non-noble metal catalytic species, said compositionconsisting essentially of:(a) a reducing agent for said non-noble metalcatalytic species, (b) a complexing agent for said non-noble metalcatalytic species, and (c) an accelerator comprising a cyanide complexof a Group VIII metal.
 2. The stabilizing composition recited in claim 1including a basic compound.
 3. The stabilizing composition recited inclaim 1 wherein said catalytic metal species is selected from Group VIIIand Group IB metals of the Periodic Table of the Elements.
 4. Thestabilizing composition recited in claim 1 wherein said catalytic metalspecies is selected from the group consisting of cobalt, iron, nickeland copper.
 5. The stabilizing composition recited in claim 2 whereinsaid non-noble metal catalytic species comprises copper.
 6. Thestabilizing composition recited in claim 1 wherein said reducing agentis selected from the group consisting of formaldehyde, paraformaldehydeand a mixture thereof.
 7. The stabilizing composition recited in claim 5wherein said reducing agent is selected from the group consisting offormaldehyde, paraformaldehyde and a mixture thereof.
 8. The stabilizingcomposition recited in claim 7 wherein said reducing agent is present inan amount of from 0.7 to 1.4 weight percent of the composition.
 9. Thestabilizing composition recited in claim 5 wherein said complexing agentis selected from the group consisting of ethylenediaminetetraaceticacid, a salt thereof and a mixture of the foregoing.
 10. The stabilizercomposition recited in claim 9 wherein said complexing agent is presentin a range of from 2.8 to 4.7 weight percent.
 11. The stabilizercomposition recited in claim 5 wherein the pH is maintained at from 12.5to 12.8.
 12. The stabilizer composition recited in claim 1 wherein saidaccelerator is selected from iron-cyanide complexes.
 13. A stabilizercomposition or a real image comprising a copper species and consistingessentially of:(a) a reducing agent for said copper species selectedfrom the group consisting of formaldehyde, paraformaldehyde and mixturesthereof; (b) a complexing agent selected from the group consisting ofehtylenediaminetetraacetic acid, a salt thereof and a mixture of theforegoing; (c) an accelerator comprising an iron-cyano complex; and (d)a basic compound in sufficient quantity to raise the pH of thecomposition to greater than pH 7.